In previous production of activated carbon from raw lignite coal, for example, using a moving grate stoker furnace, the market value of the end product suffered due to comparatively small surface area in relatively large particles. It was found that the -12 +100 mesh cut of this material compared favorably with competing activated carbon products. That portion, however, represented only about 30% of the end product and the quality of the end product was thus reduced by the +12 mesh particles because the +12 mesh particles in the end product had relatively low surface area; and this diminished the market value of the end product.
According to this invention, the +12 mesh material is stripped from the product discharging from the quench chamber and crushed to -12 mesh size, and recirculated with the new starting material passing through the chain grate stoker furnace. The crux of the invention is that merely crushing the +12 mesh end product material to -12 +100 mesh size does not increase the surface area to the extent needed to render them sufficiently active, whereas crushing and then recirculating the over-size particles does sufficiently increase its surface area and render it sufficiently active to be marketable.